Conversion of hydrocarbons



Feb. 16, 1943. H. v. ATWELL CONVERSION OF HYDROCARBONS Filed April .3, 1940 INVENTOR #419042 MAT/44524 ATTORNEY Patented Feb. 16, 1943 CONVERSION OF HYDROO'ARBONS Harold V. Atwell, Beacon, N. Y., assignor to Process Management Company,

Inc., New

York, N. Y., a corporation of Delaware Application April 3, 1940, Serial No. 327,553

2 Claims.

This invention relates to the conversion of hydrocarbons, particularly for the production of motor fuel or gasoline.

The invention contemplates a process in which a plurality of different boiling point fractions of hydrocarbon oil are subjected to separate cracking treatments and in which normally gaseous hydrocarbons are fractionated to form a plurality of fractions of different boiling points and a higher boiling fraction comprising normally gaseous hydrocarbons is combined with a higher boiling hydrocarbon oil fraction for polymerization and reaction or reversion therewith while progressively lower boiling normally gaseous fractions are combined with progressively lower boiling hydrocarbon oil fractions for polymerization and reversion or reaction therewith.

In a particular embodiment of the invention a plurality of hydrocarbon oils of difierent boiling points, such as a residual stock and one or more condensate fractions are subjected to cracking for conversion into lower boiling products including normally gaseous hydrocarbons, and such hydrocarbons are fractionated to form a plurality of fractions and a resultant higher boiling gaseous fraction is combined with the higher boiling oil fraction, such as the residual stock, while progressively lower boiling gaseous fractions are combined with progressively lower boiling oil fractions under conditions to undergo polymerization and reaction or reversion in the presence of such oil fractions.

The invention furthermore contemplates a unitary combination process for the processing of crude petroleum to maximum yields of products within the gasoline or motor fuel boiling range, in which the crude oil is fractionated to separate a residue from lighter stocks adapted for cracking, in which the residue is subjected to cracking or viscosity-breaking for conversion into intermediate components adapted for further cracking into gasoline, in which such intermediate components are combined with straight run fractions from the crude petroleum and subjected to cracking for conversion into lower boiling constituents, in which the normally gaseous hydrocarbons produced in the process are fractionated to form a plurality of fractions and the heavier gaseous fraction combined with the crude residuum in the viscosity-breaking operation for polymerization and reaction or reversion in the presence of the residual components while lighter gaseous fractions are combined with the lighter stocks or intermediate constituents for polymerization and reaction or reversion.

One aspect of the invention is concerned with an improvement in the viscosity-breaking or cracking of residual stocks and contemplates a cracking operation in which the residual stock or the normally liquid component that is charged to such cracking operation is subjected to cracking in single-passage through the cracking zone in the presence of normally gaseous constituents under conditions conducive to polymerization and reversion reactions as well as under conditions adapted for the cracking or viscositybreaking of the heavy stock. In this operation the cracking of the liquid or heavy residue is under once-through conditions but in the presence of recycled light fractions comprising normally gaseous constituents.

For the purpose of more fully disclosing the invention, reference will now be had to the accompanying drawing, which is a diagrammatic elevation of apparatus adapted for practicing a particular embodiment of the invention.

In the apparatus illustrated, crude oil charging stock, after being heated by exchange with hot products of the process or by other heating means, is introduced by pump Ill into a separator II, wherein separation of vapors from residue takes place. The residue is withdrawn through a line l2 and directed by a pump M to a heating coil 15 positioned in a furnace 16 adapted to heat the oil to a cracking temperature. The residue, together. with normally gaseous hydrocarbons, the source of which will be presently explained, is subjected to cracking temperature under superatmospheric pressure to effect viscositybreaking of residual constituents and resultant conversion into lower boiling products while the gaseous constituents are subjected to reaction and combination to form higher boiling constituents including components within the motor fuel boiling range. The resultant products of conversion are separated into vapors and residue in a separator or evaporator tower H. The tower may advantageously be formed with a fractionating section [8 so that the heavier components of the vapors may be condensed and collected in a tray l9. This primary or heavy reflux condensate may be directed by a pump 20 and line 2| to a recycling heating coil 22 positioned in a fumace 23 adapted to supply cracking temperature to the oil. The cracked products pass through a transfer line 24 to the separator 11 wherein they are separated into vapors and residue together with the products from the primary viscosity-breaking coil l5. The residue may be withdrawn through a line 25.

A vapor line 26 extending from the crude oil separator H and a vapor line 21 extending from the tower I1 serves to conduct the vapors to a common fractionating tower 28 so that the vapors from the crude oil and lighter vapors from the viscosity-breaking operation may be fractionated together. The tower 28 is equipped with conventional fractionating elements and with such cooling and refluxing means as may be desired. Reflux condensate comprising intermediate constituents from the crude oil and from the viscosity-broken products is withdrawn from the bottom of the tower 28 and directed by pump 29 to a heating coil 3| positioned in a furnace 32 adapted to heat the oil to a cracking temperature. The oil is subjected to cracking conditions of temperature and pressure in the heating coil 3| to maintain a relatively high rate of cracking per pass and effect conversion into gasoline constituents of high anti-knock quality. Normally gaseous hydrocarbons from a source which is hereinafter explained are combined with the reflux condensate undergoing cracking in the heating coil 3| and conditions favoring polymerizing and reversion reactions are maintained in the coil so as to effect conversion and combination of normally gaseous hydrocarbons into higher boiling normally liquid products. The resultant products of reaction are separated into vapors and residue in a separator or reaction chamber 33 from which the residue may be withdrawn through a line 34. The separated vapors pass to a fractionating tower 35 provided with conventional fractionating elements and such cooling and refluxing means as may be required to effect the desired fractionation. Reflux condensate maybe withdrawn from the tower 35 and cycled by pump 3,6and line 31 to the cracking coil 3|.

A light fraction such as a naphtha fraction is collected in a tray 38 of the tower l2 and this fraction is conducted by a pump 39 and line 40 to a heating coi1 4| positioned in a furnace 42 which is adapted to. supply cracking temperature to the oil in transit through the heating coil. The oil is subjected to cracking or reforming in the heating coil 4| in the presence of normally gaseous hydrocarbons, from a source which is hereinafter explained, while under conditions favoring polymerizing and reversion reactions to effect polymerization and combination of normally gaseous constituents into normally liquid constituents. The products of conversion from the heating coil 4| are separated into vapors and residue in a separator 43, from which the, residue may be withdrawn through line 44. The separator 44 is preferably provided with a reflux,. as by means of line 45, so that only vapors having the boiling points of the desired light distillate, such as gasoline, may pass overhead to a fractionating tower 46, which is provided with conventional fractionating elements and suitable cooling and refluxing means. In the tower 46 the vapors are subjected to fractionation or'rectification to form a desired condensate product, such as gasoline or naphtha, which may be withdrawn through a line 41, while uncondensed vapors and gases are withdrawn through a line 48.

Uncondensed vapors and gases from tower 28 are removed by a line 49 and uncondensed vapors and gases from tower 35 are removed by a line 50. The lines 49 and 50, as well as the line 48 from tower 46, communicate with a common line bywhich the gases and Vapors are conducted toa fractionating tower 52' provided with conventional fractionating elements and cooling and refluxing means to effect the desired fractionation. In the tower 52 the Vapors are fractionated and rectified to produce a distillate product, such as gasoline, of desired boiling point and vapor pressure. This product may be removed through a line 53. Uncondensed vapors and gases are removed through a line 54 and conducted by a compressor 55 under increased pressure through a cooling coil 55, thence to a fractionating tower 57. The latter tower is equipped with conventional fractionating elements and with heating or reboiling means 58, as well as with cooling or refrigerating means 59, to accomplish the necessary low temperature rectification so as to separate a primary or high boiling fraction comprising normally gaseous hydrocarbons which fraction may be removed as a liquid through a line 60. The line 60 may be provided with a branch line 6| so that condensate formed in the tower 5! may, if desired, be blended with the product withdrawn through line 53 from tower 52. The condensed product separated out in tower 57 will normally comprise C4 and C5 hydrocarbons. Uncondensed gases are removed from the tower 57 through a line 62 and are conducted by compressor 63 under increased pressure through a cooling coil E4 thence to a fractionating or rectifying tower 65 which is provided with conventional fractionating elements and with heating or reboiling means 66, as well as with cooling or refrigerating means 61-. Fractionation is carried on in the tower B5 to separate out as condensate an intermediate fraction of normally gaseous hydrocarbons which will normally comprise C3 and C4 hydrocarbons which fraction may be withdrawn through a line 68'. A portion of the uncondensed gases may be intermittently or continuously removed from the system through a line 89'. Uncondensed gases are also passed through a line 69 and are conducted by a compressor 10 through a cooling coil 7| thence to a fractionating or rectifying tower 52, which is provided with conventional fractionating elements and with heating or reboiling means 73, as well as with cooling or refrigerating means 14. Fractionation is carried on in the tower 12 to separate the lighter constituents, particularly the hydrogen and methane, which may be removed through a line I5, from a fraction of normally gaseous hydrocarbons which will ordinarily comprise C2 and C3 hydrocarbons, which fraction may be Withdrawn through. a line 16.

In practicing the invention the fraction withdrawn through line 60 from tower 5-1 may be conducted by a pump 71 and line 18 to the cracking or viscosity-breaking coil I5, for combination with the heaviest normally liquid oil fraction undergoing conversion and for polymerizing and reversion reactions in the presence-of such-heavy oil, the fraction of normally gaseous hydrocarbons withdrawn through line 68. from tower 65 may be conducted by a pump 19- and line 80. to the cracking coil 3t for combination, with the intermediate normally liquid oil fraction undergoing conversion therein and for polymerizing and reversion reactions in the presence of such liquid oil, while the fraction of'normally gaseous hydrocarbons withdrawn through line 16 from tower 12 may be connected; by; a pump- 81- and' line 82 to the cracking or reforming coil. 4| for combination with the lighter normally liquid: oil fraction undergoing conversion or reformingeand for polymerizing and reversion reaction in; the.

presence of such-lighter-oil.

The line 18 may be provided with a branch line 83 and the line 80 may have a branch line 84 so that a portion of one or both of the fractions from towers 51 and 65 may be conducted to the recycling cracking coil 22 for combination with the heavy reflux condensate undergoing conversion and for polymerizing and reversion reactions therein.

In fractionating the constituents lower boiling than gasoline to produce the gaseous fractions for recycling to the several reaction zones, it is advantageousto include in the heavier fraction certain hydrocarbons which, although classified as normally liquid hydrocarbons are nevertheless of lower boiling point than gasoline such as C hydrocarbons, so. that these very low boiling normally liquid hydrocarbons, particularly the olefins such as amylene may be converted into constituents of somewhat higher boiling point well adapted for inclusion in the gasoline product.

The gases produced as a result of the'sever'al cracking steps of the process will be character, ized by having a relatively high olefinic content. While the normally gaseous olefins will be readily reactive under the conditions obtaining in the several cracking zones to form conversion products of higher boiling point within the normal gasoline boiling range, the paraflinic hydrocarbons will be somewhat less reactive in this respect. It is accordingly desirable to provide for the release from the system of some of the normally gaseous constituents in addition to the methane, so as to prevent an' undue concentration of parafiinic gases in the system. The re lease line 69' is advantageous to efiect removal from the system of a certain proportion of the C2 hydrocarbons so as to prevent an undue concentration of ethane building up in the system. A certain proportion of these gases may be continuously released through the line 69' or the line may be operated intermittently to provide for the release of ethane hydrocarbons.

In practicing the invention it is desirable to maintain pressures of the order of 500 pounds or higher in the several cracking zones in order to promote the reactions of the normally gaseous constituents resulting in the formation of hydrocarbons of higher boiling point within the gasoline range. The temperatures employed in the several reaction zones wherein the normally liquid and normally gaseous constituents are in reactive contact are adapted to support cracking conditions to effect conversion of liquid components into lower boiling constituents including hydrocarbons within the gasoline boiling range and to effect polymerization of normally gaseous hydrocarbons, particularly olefins, into higher boiling constituents including constituents within the gasoline boiling range as well as to support reversion reactions adapted to efiect an increase in the gasoline yield.

Temperatures of about 900 F.-950 F. under pressures of 500 to 1,000 or 2,000 pounds are recommended for the viscosity breaking zone l5, in which the crude oil residuum and the heavier normally gaseous fraction comprising C4 and C5 hydrocarbons are subjected to conversion conditions. When the heavy condensate cracking zone 22 is used in the process, fractionating conditions are maintained in the tower l8 so as to withdraw a heavy fraction from the tray [9 having an initial boiling point of the order of 600 F.-700 F. and consisting essentially of components distilling within a range of 700 F. to 800 F. or 850 F. (as determined by a vacuum distillation and interpolated to an atmospheric pressure basis); This heavy fraction is subjected to temperatures of 900 F.-950 F. under pressures of 500 to 1,000 pounds, in the presence of recycled heavier normally gaseous hydrocarbons'such as C; hydrocarbons, or in the presence of intermediate gases such as C3 or C4, hydrocarbons, or a mixture of such heavier and intermediate gaseous constituents. The gas oil fraction which is subjected to cracking in the cracking zone 3| is heated thereinto temperatures of 950 F.1000 F. under pressures of 500 to 1,000 pounds in the presence of the recycled intermediate gaseous fraction comprising essentially C3 and C4 hydrocarbons to accomplish cracking into lower boiling components within the gasoline. boiling range as Well as conversion of normally gaseous hydrocarbons into higher boiling components within the gasoline boiling range. The gas, oil subjected to conversion in cracking zone 3| will have a lower specific gravity than thatof the heavy condensate subjected to conversionin cracking zone 22 and will ordinarily consist essentially of constituents distilling within a range of 400 F. or 450 F. up to 650 F., 700 F. or'750 F., The naphtha fraction which is subjected to reforming in the presence of the lighter, recycled gases such as C2 and C3 hydrocarbons will ordinarily have an initial boiling point of 200 F.-300 F. and an end point of 400 F. to 450 F. or 500 F. This fraction is subjected to temperatures of 1000 F.-1050 F. under pressures of 1,000 to 2,000 pounds to effect reforming of the gasoline hydrocarbons into constituents of higher antiknock quality and simultaneously effect conversion of normally gaseous hydrocarbons into higher boiling hydrocarbons within the gasoline boiling range.

In a specific example of the invention, crude oil is fractionally distilled to form a residue, a

gas oil fraction of approximately 750 F. end' point, a heavy gasoline or naphtha fraction distilling between 250 F. and 425 F., and a light gasoline fraction having an end point of approximately 300 F. The residue is subjected to conversion under viscosity breaking conditions in the presence of a recycled fraction consisting essentially of C4 and C5 hydrocarbons at a temperature of 925 F. under 750 pounds pressure. A gas oil fraction of approximately 700 F. end point is recovered from the viscosityibroken products and combined with the straight run gas oil fraction. The mixture is subjected to cracking temperature of 975 F. under 800 pounds pressure, in the presence of a recycled gaseous fraction consisting essentially of C3 and C4 hydrocarbons. The straight run heavy gasoline or naphtha fraction is subjected to reforming at a temperature of 1020 F. under 1000 pounds pressure in the presence of recycled C2 and Ca hydrocarbons.

In a modification of the invention the normally gaseous constituents from the crude oil distillation are separately recovered and passed to a cracking zone wherein they are subjected to high temperature conditions adapted to effect conversion into olefim'c constituents. The resulting normally gaseous constituents may then be fractionated, as in the towers 51, 65 and T2 to obtain the desired fractions for recycling.

While I have described a particular embodiment of my invention for purposes of illustration, it should be understood that various modifications and adaptations thereof which will be obvious to one skilled in the art, may be made withgasoline, subjecting said lower boiling constituents to further fractionation together with vapors produced in the crude oil distillation so that components thereof are combined with said lighter and heavier fractions, passing said higher boiling constituents to a second cracking zone wherein they are subjected to cracking conditions of ternperature and pressure to effect conversion into gasoline constituents, fractionating the resultant cracked products together with the viscosity broken products from the first cracking zone, di-

recting said heavier fraction to a third cracking zone wherein it is subjected to cracking, directing said lighter fraction to a fourth cracking zone wherein it is subjected to cracking, subjecting the second cracking zone to a cracking temperature,

subjecting the third cracking zone to a higher cracking temperature, subjecting the fourth cracking zone to a still higher cracking temperature, fractionating vapors evolved from said third and fourth cracking zones to separate a fraction comprising gasoline from lighter components comprising normally gaseous hydrocarbons, subjecting such lighter components comprising normally gaseous hydrocarbons to fractionation to .form heavier, intermediate and lighter normally gaseous fractions, combining said heavier gaseous fraction with the aforesaid residual fraction for conversion therewith, combining said intermediate gaseous fraction with the aforesaid heavier fraction for conversion therewith, combining said lighter gaseous fraction with aforesaid lighter fraction for conversion therewith and maintaining conditions of temperature and pressure in each of said cracking zones adapted to effect conversion of normally liquid and normally gaseous hydrocarbons into components within the gasoline boiling range.

2. In the conversion of hydrocarbons to form gasoline hydrocarbons the process that comprises separately distilling crude petroleum to form a residual fraction and vapors and fractionating the vapors to form lighter and heavier fractions, directing said residual fraction to a first cracking zone wherein it is subjected to cracking under viscosity breaking conditions, directing the resultant viscosity broken products into a separating zone wherein vapors separate from residue, separately fractionating the separated vapors from said separating zone to separate a higher boiling reflux condensate from lighter constituents com-prising components higher boiling than gasoline, combining such lighter constituents with vapors from the crude oil distillation to subject such constituents to further fractionation together with vapors produced in the crude oil distillation so that components thereof are combined with said lighter and heavier fractions, .passing said higher boiling reflux condensate to a second cracking zone wherein it is subjected to cracking conditions of temperature and pressure, directing the resultant cracked products to said separating zone, directing said heavier fraction to a third cracking zone wherein it is subjected to cracking conditions of temperature and pressure, directing said lighter fraction to a fourth cracking zone wherein it is subjected to cracking conditions of temperature and pressure, fractionating vapors evolved from said third and fourth cracking zones to separate a fraction com-prising gasoline fromlighter components comprising normally gaseous hydrocarbons, subjecting such lighter components comprising normally gaseous hydrocarbons to fractionation to form heavier, intermediate and lighter normally gaseous fractions, directing a portion of said heavier gaseous fraction to said first cracking zone and directing another portion thereof to said second cracking zone, combining said intermediate gaseous fraction with the aforesaid heavier fraction for conversion in said third cracking zone, combining said lighter gaseous fraction with the aforesaid lighter fraction for conversionv inv said fourth cracking zone and maintaining conditions of temperature and pressure in each of said cracking zones adapted to effect conversion of normal- 1y liquid and normally gaseous hydrocarbons into, components within the: gasoline boiling range.

HAROLD V. .ATWELL; 

